In general, an aircraft nacelle has a structure comprising an air inlet structure, a median structure and a downstream structure. The term “downstream” here refers to the direction corresponding to the direction of the cold air flow penetrating the turbojet engine. The term “upstream” refers to the opposite direction.
The nacelle has a downstream jet nozzle whereof the outlet is situated downstream of the turbojet engine. Further upstream, the downstream section generally houses thrust reverser means intended to surround the combustion chamber of the turbojet engine. The median structure is positioned downstream of the air inlet structure so as to surround the fan of the turbojet engine. The air inlet structure is situated upstream of the turbojet engine serving to propel the aircraft.
The air inlet structure comprises, on one hand, and air inlet lip and, on the other hand, a downstream structure on which the lip is fastened. The air inlet lip is adapted to allow the optimal collection towards the turbojet engine of the air necessary to power the fan and the internal compressors of the turbojet engine. The downstream structure is intended to suitably channel the air towards the vanes of the fan. This downstream structure generally includes an external panel and an internal panel. The internal panel includes an acoustic shroud making it possible to attenuate the noises created by the turbojet engine as well as the vibrations of the structures. The downstream structure and the air inlet lip are fastened upstream of a casing of the fan belonging to the median structure of the nacelle.
Depending on the temperature and relative humidity conditions on the ground or in flight, frost can form on the profile of the lip, in particular at the inside profile. This frost formation can be dangerous for the mechanical operation of the stationary and rotating portions of the turbojet engine and cause a decrease in performance. Deicing systems for this part of the air inlet lip have therefore been developed to resolve this problem.
Currently, maintenance operations on this equipment housed inside the air inlet structure require builders to provide access holes for accessing this various equipment. However, these holes are not always sufficient. It is thus sometimes necessary to verify the internal equipment of the air inlet structure using specific tools, such as an endoscope. Such specific tools do not always enable a satisfactory monitoring.
Moreover, to replace some of the internal equipment, it is in general necessary to place the entire air inlet structure. Such a placement requires significant tools and causes an immobilization of the propulsive assembly and therefore generally of the airplane.
An air inlet structure has been proposed formed by an external panel fastened to the air inlet lip and at least one internal panel fastened to the casing of a median structure. The air inlet structure is translationally mobile relative to the median structure using a system of rails fastened on the acoustic shroud. At the end of maintenance to close the air inlet structure on the median structure, it is known from application FR 06-08599 (publication number FR 2 906 568) to use a centering device in the form of a centering pin in order to guide the closing along an axis of the air inlet lip on the acoustic shroud.
However, the covering of the air inlet lip and the acoustic shroud as well as the alignment of the centering pin relative to the receiving bore must be very precise to prevent any friction or jamming of a nature to prevent the closing of the air inlet lip on the acoustic shroud.
It is also known from applications FR 08-00265 and FR 08-00560 to use additional locking means positioned respectively behind or in front of the centering device.
However, the association of the centering device and locking means requires very precise geometries of the parts to limit the play between the air inlet lip and the acoustic shroud in order to ensure good centering and also a good pick-up of mechanical stresses. Such a configuration causes a relatively high production cost.